Moire on print but not on PDF? What to do?

I have moire on these images even-though it looked perfect before print? Is there a way i can make a preview that reveals the "hidden" moire?

I view it in printview on photoshop(calibrated to my imac screen) "there was a little moire" then saved it as PDF "then no moire" opened pdf in same size as printsize. How can something looking perfect turn out so wrong?